Intake Manifold

Intake manifold is the pipe network structure in an internal combustion engine that distributes fresh air (and fuel mixture in some systems) evenly to the engine cylinders.

Its function is to connect the throttle body (or carburetor) with the intake ports on the cylinder head, ensuring that each cylinder receives a balanced air or air-fuel mixture.

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The intake manifold is a critical component that directly affects engine performance. Its main functions are:

• Evenly distribute air and fuel mixture: In carbureted engines (wet manifold), it is essential that the fuel remains fully mixed and reaches all cylinders equally without separating.
• Optimize air flow: In modern fuel-injected engines (dry manifold), only air is carried, allowing for more complex and aerodynamic designs.
• Increase volumetric efficiency: By managing air flow velocity and density, it enables the engine to produce more power.

Air, after passing through the air filter and throttle body, enters a chamber known as the "plenum." From there, it is distributed through individual pipes called "runners" that lead to each cylinder. The plenum volume and runner length are decisive factors in determining the engine's power characteristics.

• Wet manifold: Used in carbureted engines. It carries the air-fuel mixture. Its internal surfaces must be smooth with gentle bends.
• Dry manifold: Used in fuel-injected engines. It carries only air. More complex and performance-oriented designs are possible.

The intake manifold consists of several main sections:

• Plenum: The central chamber that supplies all runners.
• Runners: Individual pipes that connect the plenum to the intake ports of each cylinder.
• Throttle Valves (in some designs): In variable-length manifold systems, internal mechanisms are included to alter airflow for high and low engine speeds.

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Key criteria considered when designing an intake manifold:

• Airflow resistance: Wider pipes offer less resistance but can weaken airflow at low engine speeds. Therefore, runner diameter is optimized according to engine dynamics.
• Runner length:
• • Long runners → Deliver higher torque at low engine speeds.
  • Short runners → Deliver higher horsepower at high engine speeds.
• Plenum volume: Large plenum → Better power at high engine speeds; small plenum → Improved throttle response.
• Fluid mechanics principles: Losses at the inlet and outlet points (major and minor losses) are minimized.
• Pressure waves and resonance effects: In high-performance engines especially, pressure waves generated during the intake process are harnessed to increase cylinder filling. (wave tuning).